Boiler size sufficient or not?

[M Gaffar]

Calling on the knowledge of any plumbers out there.

I am about to have an extension done and am looking for some guidance on whether my current boiler will be able to cope with the extra additions. I appreciate people may not be able to give me a definitive answer but something along the lines of a) definitely need bigger boiler b) may be sufficient but need plumber to do calculations and confirm c) should be ok d) more than enough

The current setup is;

3 bed semi, boiler is vaillant model no. vcw gb 242 eh, nominal input 101030 BTU(28.8KW), nominal output 81900 BTU (24KW), burner press mbar 5.1

Front room 15ft by 11.9ft with standard double panel radiator Lounge 20.5ft by 11.8ft with standard double panel radiator and patio door to garden kitchen 15.5ft by 7.5ft no radiator Bedroom 1 & 2 12ft by 11ft with standard double panel radiators, Bed 3

8ft by 7ft with standard double panel radiator bathroom 6.5ft by 6.5ft with standard single panel radiator entrance hallway with standard double panel radiator

After extension, in addition to the above there will be new downstairs toilet and basin radiator in kitchen (15ft by 13ft) (approx 6000 BTU) radiator in study (10ft by 5.8ft) downstairs (approx 2000BTU) radiators in bedroom 4 and 5 (10ft by 5.8ft & 15ft by 5.8ft) (approx

1400BTU & 2000 BTU) ensuite shower room (6ft by 6ft) with radiator (approx 1400BTU), shower may be electric, not decided larger bedroom 2 (extended by further 9ft by 8 ft)

Any comments/advice appreciated

Thanks BS

[Andy Hall]

It is much easier if you stick to one system of units (which should be SI, so dumping deprecated BTUs, feet etc. and using metres and watts.) It's very easy to make mistakes otherwise.

A simple solution would be to download the radiator calculation programs from the Barlo radiators web site, or I can email you the Myson one.

You need to know the wall and window materials and types because this makes a huge difference.

Plug the numbers in and it will give you heat loss per room.

.andy

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[burbeck]

hi try this

[Set Square]

My hunch is that it's ok - unless the house is very poorly insulated.

To be sure, it needs calculating properly - using the appropriate U values for all walls, windows, floors, ceilings, etc. The U values are heavily dependent on the type of wall construction, glazing, and standards of insulation employed.

[Christian McArdle]

It also depends on the insulation. However, if it is an old house with poor insulation and you are bolting on a new insulated extension to building regulations, it is actually possible that the total heating requirement goes down, as the entire extension is actually less leaky than the old uninsulated wall.

In any case, 24kW should be enough for any semi-detached. Combi boilers (and modern system ones) are generally sized to provide sufficient hot water capacity. The heating capacity is usually a fraction of the output power. If it isn't, the correct procedure is not to replace the boiler, but to improve your insulation. This would be vastly cheaper in materials and would save a fortune in energy costs, far more even than the benefit of replacing a traditional with a condensing boiler.

If you've got an uninsulated cavity, even better. Don't even consider failing to insulate the cavity whilst you're having the work done. The final resulting building will probably require less than half the heating of the previous poorly insulated house.

Christian.

[IMM]

Half?

The whole existing loft would need thicker insulation. Insulating a cavity in what is now an internal wall. will help, not a great deal. It will prevent cold air circulating between the house and extension from the other cavities.

Best have cavity wall insulation all cavities if doing an extension anyway, with 1 foot of insulation in the loft.

[Christian McArdle]

Perhaps I didn't make myself clear. I meant cavity insulating the entire original house, not just the dividing wall.

Christian.

[m.gaffar]

Thanks for all the replies, The feeling seems to be it should be able to cope as is confirmed by the useful website link posted above. I'll also be making sure the insulation for the existing house is looked at once the building work is underway

Just whilst I'm on the topic, is a Corgi registered engineer required to resite the boiler (I'll be moving it from upstairs bathroom to downstairs utility room) or can any competent plumber do this? Builder has included this in his list of jobs to do but has confirmed the engineer is not Corgi registered, but very experienced and used by him for all his jobs

Thanks

[Andy Hall]

It would be illegal for an unregistered plumber to do this however experienced he is.

You could do it as a DIY job if you are competent, but for a job done for gain, a registered CORGI engineer is the only legal option. You wouldn't be in trouble for using him unless there were a problem and it came out that you knew that he was unregistered (your insurance might not pay up). The plumber could be fined, however.

.andy

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[M Gaffar]

Thanks Andy, another one to tackle the builder with

[Christian McArdle]

However, most of the work could be done by the person, provided that the gas work part and the commissioning was done by a CORGI. The majority of work resiting a boiler consists of rerouting the water pipework and electrics, mounting the boiler to the wall and creating a suitable path for the flue to run through. The CORGI can then come in, route the gas pipe, install the flue and commission the boiler.

Christian.

[Dave Plowman (News)]

That's very strange. For quite some time now, anyone working on gas as a job or part of it has had to be CORGI registered by law. For your builder to use someone who isn't lays both of them open to prosecution. I hope your builder isn't equally as lax with other legal requirements.

[M Gaffar]

It's something I'll be picking up with him, I've already spoken to the local building inspectors (not about this particular issue, but his work in general), and the 2 that have had to assess his jobs so far have never had any problems with his work.

Regards

[Andy Hall]

All true. However finding a CORGI fitter willing to just do a small part of the job and then take legal responsibility for the complete installation may not be so easy.

For example, I have spoken to some who will not touch a job like this without doing a complete gas pipe run all the way back to the meter on the argument that they can see the work for which they are responsible. The same with flue installation.

It is a seller's market.......

.andy

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[Gaffar]

Thanks for all the replies guys, I have spoken to the builder now and he has confirmed that his plumber is not Corgi registered but (as suggested on here) he does most of the pipe and fitting work and he has a contact who is Corgi registered who does the gas commisioning and decommisioning, then checks the rest of the installation and provides the certificate.

Is there anything wrong with this approach?

Regards

[Dave Plowman (News)]

No. Just seems odd for a pro setup.

[Owain]

"Gaffar" wrote | Thanks for all the replies guys, I have spoken to the builder | now and he has confirmed that his plumber is not Corgi registered | but (as suggested on here) he does most of the pipe and fitting | work and he has a contact who is Corgi registered who does the | gas commisioning and decommisioning, then checks the rest of | the installation and provides the certificate. | Is there anything wrong with this approach?

Depends. If the 'contact' is CORGI registered on his own account and is properly invoicing the plumber who is invoicing the builder who is invoicing you, then the CORGI registration is valid and the plumber (and thus eventually you) should be covered by his insurances. Remember too that his CORGI registration must be valid for the classes of work he is doing; someone certified for fish fryers isn't necessarily allowed to touch domestic boilers or water heaters. Ed Sirett's FAQs are floating around cyberspace somewhere.

If however the 'contact' is CORGI registered to his employer and is doing work on the black, his CORGI registration (and his employer's insurances) will NOT cover him (and thus you). A particular problem I've encountered seems to be local authority housing gasfitters doing work on the black.

Owain